1. Field of the Invention
The present invention relates to a wire dot printer, a wire dot printer head used for this and an armature used for this, and more particularly to an armature formed by laminating plural flat plates, a wire dot printer head using this and a wire dot printer.
2. Discussion of the Background
There has been known a wire dot printer head wherein an armature with a printing wire coupled thereto is pivoted between a printing position and a stand-by position, and when the armature is pivoted to the printing position, a tip of the wire is brought into collision with a printing medium to effect printing. In a certain wire dot printer head of this type, there has been proposed a device wherein a magnetic flux is produced by a coil around the armature, that is to be pivoted, for forming a magnetic circuit that causes the armature to be attracted from a stand-by position to a printing position to effect printing.
In the wire dot printer head described above, the armature has an arm supporting the wire and a magnetic circuit forming member provided at the arm for forming a magnetic circuit. The magnetic circuit forming member is generally welded to the arm by a spot welding.
On the other hand, it has been known that an eddy current loss is caused by a ripple (change) in a flux passing through the magnetic circuit forming member. In order to restrain the eddy current loss to prevent the deterioration in magnetic characteristic, there has been proposed a technique for forming an armature by laminating plural thin plate-like members (see JPA Hei-2(1990)-11336). JPA Hei-2(1990)-11336 discloses that plural plate-like members are coupled together with an engagement to integrally form an armature. The space between these plural plate-like members is spot-welded to be joined together.
When a spot welding is used for welding plural plate-like members, sufficient joining force cannot be obtained since sufficient pressure cannot be applied to these members. Therefore, plural plate-like members are not at all joined, or even if they are joined once, they do not withstand the pivotal movement of the armature during the printing operation, resulting in disassembly. Further, pressure is applied to the plural plate-like members during the spot welding, so that these members are sometimes deformed. Moreover, as shown in FIG. 7, weld zones (nuggets) 101 are produced on the plate-like member 100 due to the spot welding. The weld zones 101 reaching a path of magnetic flux (in the vicinity of arrows in FIG. 7) become a factor for deteriorating magnetic flux characteristic in the magnetic circuit.
On the other hand, the armature disclosed in JPA Hei-2(1990)-11336 is formed such that plural plate-like members are coupled together with an engagement, so that a gap is present between the adjacent plate-like members, thereby deteriorating adhesion. Further, it is difficult to decrease a dimensional tolerance at the engagement section, so that the adhesion goes on deteriorating. This reduces magnetic characteristic of the magnetic circuit, whereby the stabilized pivotal movement of the armature cannot be realized, and further, magnetic characteristic required for high-speed printing cannot be obtained. As a result, it is impossible to execute high-speed printing. In particular, the armature is required to be pivoted 2500 times per second between the printing position and the stand-by position with a recent increased printing speed. Therefore, the deterioration in the magnetic characteristic becomes an important problem. Further, a welding operation is performed for welding the gap between plural plate-like members in the technique disclosed in JPA Hei-2(1990)-11336, so that it is impossible to join plural plate-like members en bloc, thereby increasing the working time of the welding operation.